Abstract

A wide variety of astrophysical observations indicate that approximately 85% of the matter in the universe is nonbaryonic and nonluminous. Understanding the nature of this "dark matter" is one of the most important outstanding questions in cosmology. Weakly Interacting Massive Particles (WIMPs) are a leading candidate for dark matter since they would be thermally produced in the early universe in the correct abundance to account for the observed relic density of dark matter. If WIMPs account for the dark matter, then rare interactions from relic WIMPs should be observable in terrestrial detectors. Recently, unexplained excess events in the DAMA/LIBRA, CoGeNT, and CRESST-II experiments have been interpreted as evidence of scattering from WIMPs with masses ~10 GeV and spin-independent scattering cross sections of 10-41-10-40 cm2.

The Cryogenic Dark Matter Search (CDMS II) attempts to identify WIMP interactions using an array of cryogenic germanium and silicon particle detectors located at the Soudan Underground Laboratory in northern Minnesota. In this dissertation, data taken by CDMS II are reanalyzed using a 2 keV recoil energy threshold to increase the sensitivity to WIMPs with masses ~10 GeV. These data disfavor an explanation for the DAMA/LIBRA, CoGeNT, and CRESST-II results in terms of spin-independent elastic scattering of WIMPs with masses ≲12 GeV, under standard assumptions. At the time of publication, they provided the strongest constraints on spin-independent elastic scattering from 5-9 GeV, ruling out previously unexplored parameter space.

To detect WIMPs or exclude the remaining parameter space favored by the most popular models will ultimately require detectors with target masses ≳1 ton, requiring an increase in mass by more than two orders of magnitude over CDMS II. For cryogenic detectors such as CDMS, scaling to such large target masses will require individual detector elements to be fabricated more quickly and cheaply, while maintaining the nearly background-free operation of the existing experiment. We describe the development of athermal phonon mediated particle detectors using Microwave Kinetic Inductance Detectors (MKIDs), which could provide a simpler path to extending the CDMS detector technology to the ton scale. Results from prototype devices have demonstrated energy resolutions as good as σ = 0.55 keV at 30 keV, comparable to existing CDMS II detectors. Such designs can be scaled to kg-scale detector elements, while reducing the complexity of the detector fabrication and cryogenic readout electronics relative to existing designs. Since MKIDs are naturally multiplexed in the frequency domain, MKID-based designs also allow much finer pixelization of the phonon sensor, which is expected to enhance background rejection for large detectors while simultaneously reducing the number of wires needed to read out the detectors.